Active Flow Control A Tool to Improve System Efficiency

Transcription

1 Active Flow Control A Tool to Improve System Efficiency Prof. Miki Amitay Mechanical, Aerospace and Nuclear Engineering Rensselaer Polytechnic Institute Troy, NY Special Thanks to: Florine Cannelle, Marcus Ciuryla, John Farnsworth, Kiyoshi Otani, Anna Pavlova, David Tamburello Bill Gressick (CATS), John Wen (CATS) 1

2 Flow Control Flow control: Any mechanism or process through which the flow is caused to behave differently than it normally would. passive active Flow control mechanisms Turbulators / surface roughness Unsteady blowing Oscillating ribbon or flap Internal and external acoustic excitations Oscillating surface Synthetic jets (f act ~ 10. f l natural, jet ~ l char ) f act ~ f natural (f shed ) Applications Aerodynamic performance and flight control (manned and unmanned aerial vehicles) Internal flows (separation, head losses) Heat transfer control (electronic/film cooling) Mixing enhancement (combustion, noise) Renewable energy (wind turbine blades) 2

3 Synthetic Jet Glezer & Amitay, Synthetic Jets, Ann. Rev. Fluid Mech., 2002, 34: Amitay & Cannelle, Evolution of Finite Span Synthetic Jets, Phys of Fluids 18, 2006 Orifice size: Length: O(mm) Width: less than 1mm Operating frequencies: O(100Hz)-O(10KHz) Piezoelectric disk Zero-net-mass-flux (ZNMF) Allows momentum transfer to the flow Diaphragm and cavity are driven near resonance Small electric power input No plumbing or any mechanical complexity is needed The interaction of the synthetic jet with a cross flow can form a quasi-steady recirculation region Improve aerodynamic performance of lifting surfaces. 3

4 Past and Ongoing Research at FCRL 2-D Circular Cylinder baseline w/control Separation Control on 2-D Airfoils baseline w/control Stingray UAV Mini Stingray Mini UAV µuav NAVs Cessna 182 Active Electronic Cooling Active Control of Particle-Laden Jets Baseline w/ control (b) 100m/s 4

5 UAVs - Applications Police, Fire and Rescue Support Chemical-Biological Monitoring Disaster Management Caves 5

6 Flying BAGEL Model: Design Ducted fan configuration A single moving part fixed pitch propeller Flow control on the stator blades Two mini UAVs were built: Flying model Stationary model LIFT DRAG Nominal, Jets off Jets Activated 6

7 The Flying Bagel Mini UAV MOVIE 7

8 Micro Flying BAGEL MAVs are limited to and a gross takeoff weight of 100gr. Active Flow Control Flight control is achieved by active control of the flow over the stators. Two 20mm 3kHz piezo-discs are installed in each stator (~0.2W each). Technical support from the CATS in hardware and software. Closed loop control will be provided by the CATS 8

9 Flow Field over the Stator - PIV Baseline Actuated Synthetic Jet Only 9

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11 Design and Fabrication of UAVs with Synthetic Jets Design and Fabrication of Cessna 182 RC model with Synthetic Jets Instrumented Wingtips for Roll and separation Control Synthetic jets Cessna RC Model (1/6.65 of Original Cessna 182) Cessna Wing tip with synthetic jet actuators 11

12 Flight Control and Flow Control on a Cessna 182 Wing span = 18in Wing chord = 2.5in Re = 150,000 f act = 1,100 Hz (f char = 50Hz) Ciuryla et al., Journal of Aircraft, March 2007 x sj C 12

13 Flight Control Using Synthetic Jets C µ C r C 0.6 L α C µ = 0 C µ = 1.74x10-3 C µ = 4.91x10-3 C µ = 1.06x10-2 C µ = 2.62x C µ Proportional separation and roll control authority at a wide range of α. Roll moments are comparable to conventional ailerons. Small-scale synthetic jets yield a global effect. Flight tests of a 5ft RC model are underway (electronics designed by CATS). Flight tests with flow control are planned for fall

14 Separation Control Closed Loop The angle of attack was increased slowly from 0 o to ~8 o (until flow separated) The RMS output of the shear stress sensor was monitored, and when RMS threshold was reached the synthetic jets were activated by the computer. RMS threshold = 0.5V RMS threshold = 0.25V RMS threshold = 0.1V Shear Stress Sensor Output (V) Onset of Separation Roll torque reading Automatic Activation of SJ Complete reattachment Roll torque Reading Roll torque reading t (s) α

15 Applications Active Control of Sprays Explore the feasibility of using active flow control on sprays using synthetic jet actuators. Spray Cooling (cooling of electronics components) Agriculture (applying pesticides) Homeland Security (subways, trains, planes, etc.) - Sarin gas attack on the Tokyo subway in 1995 Global behavior PIV Velocity field RMS levels Direction (vectoring) Detailed characteracteristics Shadowgraphy & PTV Droplet size Droplet distribution Droplet concentration Droplet velocity Use active flow control on sprays to improve the performance of spray cooling 15

16 Experimental Setup Spray Facility Air-assisted atomizing water spray Q a Q w Q a Q w = air to water flow rate ratio can be varied by: (i) the air pressure, (ii) the water intake level WRT the spray nozzle level, L w. Damper Constant water level reservoir L w Flow control module Synthetic jets Water siphoned in Air Atomizing spray nozzle Flow meter Valve Pump Water level meter Enclosure Air filter Air desiccant Water reservoir Compressed air 16

17 Movies of Ramped and On-Off Flapping SJ Spray 1 SJ 2 ramped flapping on-off flapping 1 0 d ab c SJ 2 e SJ 1 f 1 0 SJ 2 SJ t/t p t/t 1.0 p 17

18 Spray Cooling Water Air spray nozzle Three flow control schemes: (i) all 4 jets on, (ii) ramped flapping, and (iii) on-off flapping H 50 Insulated heater Thermocouples H/d s = 35.3 Q a /Q w =166 Enclosure q [W/cm 2 ] Copper heater Cartridge heater Ceramic fiber insulation 20 w/ flow control baseline 4 jets ramped on-off T = T s -T ( o C) 18

19 Conclusions Synthetic-jet-based active flow control can be used for flight control of small-size UAVs, in lieu of (or in addition to) conventional control surfaces. Synthetic jets can be used to control sprays Global and detailed spray characteristics were modified such that the efficiency of spray cooling was improved. 19

20 Questions? 20